Scoliosis is a disorder that causes an abnormal curve of the spine, or backbone. Patients with scoliosis develop abnormal curves to either side of the body's median line (lateral curve) and the bones of the spine twist on each other like a corkscrew. Scoliosis is about two times more common in girls than boys. It can be seen at any age, but it is most common in those over 10 years old.
Often, the cause of scoliosis is unknown and is described based on the age when scoliosis develops. If the person is less than 3 years old, it is called infantile idiopathic scoliosis. Scoliosis that develops between 3 and 10 years of age is called juvenile idiopathic scoliosis, and people that are over 10 years old have adolescent idiopathic scoliosis.
In functional scoliosis, the spine is normal, but an abnormal curve develops because of a problem somewhere else in the body. This could be caused by one leg being shorter than the other or by muscle spasms in the back. In the neuromuscular form, there is a problem during the formation of the bones of the spine. Either the bones of the spine fail to form completely or they fail to separate from each other. This type of scoliosis may develop in people with other disorders including birth defects, muscular dystrophy, cerebral palsy, and Marfan's disease. This type of scoliosis is often much more severe and needs more aggressive treatment than other forms of scoliosis. Degenerative scoliosis occurs in older adults. It is caused by changes in the spine due to arthritis. Weakening of the normal ligaments and other soft tissues of the spine combined with abnormal bone spurs can lead to an abnormal curvature of the spine.
Adolescent idiopathic scoliosis is the most common form of scoliosis. If the angle of the spinal curve (Cobb's angle) is small when first diagnosed, it can be observed and followed with routine X-rays and measurements. If the curve stays below 25 degrees, no other treatment is usually needed. If the curve is between 25-40 degrees, a brace may be recommended. If the curve is greater than 40 degrees, then surgery may be recommended. Braces are not designed to correct the curve. They are used to help slow or stop the curve from getting worse.
Spinal fusion is one surgical procedure that may be used to alleviate scoliosis. In this procedure, bone is grafted to the vertebrae to form a rigid column. The rigidity of the column will prevent the curve from worsening. However, the rigid column reduces the range of motion available to the patient.
Modern surgical procedures attempt to address sagittal imbalance and rotational defects unresolved by the earlier rod systems. They primarily involve a combination of rods, screws, hooks, cables and/or wires fixing the spine and applying forces to the spine to correct the spinal curvature. An example of the use of screws and cables is seen in U.S. Patent Application Publication No. 2006/0195090 to Suddaby (“Suddaby”) which is hereby incorporated by reference in its entirety. Suddaby discloses a system for improving the alignment of a spine by placing a series of screws or pins into the posterior or lateral side of the bodies of individual vertebrae. Hollow spacers are placed between the pins and a cable is extended through the heads of the pins and the spacers and is attached to an expansion sleeve. Tension is applied to the cable by pulling it through the expansion sleeve and then applying tension to the cable to pull the attached pins into an improved alignment. One of a plurality of nodules at the end of the cable is then placed into the passage of the expansion sleeve thereby holding the cable in the new “tensioned” position. The tension discourages movement of the spine.
U.S. Pat. No. 6,551,320 to Lieberman (“Lieberman”), hereby incorporated by reference in its entirety, discloses an apparatus for aligning a spine that includes a plurality of anchors screwed into adjacent vertebral bodies. A cable or series of cables is strung through or around the anchors and then pulled. The tension applied to the cable(s) is used to pull the spine into a desired alignment. U.S. Patent Application Publication No. 2009/0112262 to Pool, et al. (“Pool”), hereby incorporated by reference in its entirety, discloses a system in which at least one anchor is screwed or otherwise embedded into an upper vertebra and one or more anchors are similarly placed in lower vertebra(ae). A cable is extended between the anchors and force applied to the cable by a magnetic adjustment device to align the spine. In some cases a second anchor-cable arrangement can be used on the opposite side of the spine.
Finally, U.S. Pat. No. 5,782,831 to Sherman, et al. (“Sherman”), hereby incorporated by reference in its entirety, discloses a system for reducing a displaced vertebra between adjacent vertebrae. The Sherman patent describes a system in which two anchors are screwed into the vertebrae on either side of the displaced vertebra with a rod attached between the anchors. A third anchor is screwed into the displaced vertebra and attached to a cable. A cable tightening device, such as a come-along type device is used to pull the displaced vertebra into alignment after which it is attached to the support rod. However, the attachment of a bar across three adjacent vertebrae prevents pulling a curved spine into a more proper alignment.
In attempting to solve spinal alignment and displacement problems, the prior art relies on multiple vertebral anchors and the application of alignment force through complicated force applicators and cable systems. Often such corrective systems fail to provide complete correction of spinal alignment as full recuperation requires either too much force to correct the curve or sudden, rapid stretching of spinal neural elements resulting in permanent neurological damage.
What is needed then is an apparatus for aligning the spine that possesses few parts and is easy to implant while enabling a gradual restoration of the of spinal alignment over a determined period of time so that large and/or sudden forces are not applied to the curved spine. By applying reduced corrective forces over a longer period of time, complications such as bone fracture and nerve damage can be reduced or avoided.